This invention relates to a synchronization judging circuit, in particular, to a synchronization judging circuit used in a W-CDMA (Wideband Code Division Multiple Access) portable terminal to judge, by the use of DPCCH (Dedicated Physical Control Channel)/DPDCH (Dedicated Physical Data Channel), whether synchronization is established or not.
A related portable terminal (or cellular phone) judges synchronization to be out and suspends transmission when a quality of DPCCH/DPDCH deteriorates under a first prescribed level. The portable terminal judges that the synchronization is established again and resumes the transmission when the quality of the DPCCH/DPDCH increases above a second prescribed level.
Concretely, the portable terminal measures DPCCH_Ec/Ior as the quality at every frame in a case where Ior/Ioc is equal to −1 [dB] at a receiving end thereof. The portable terminal judges the synchronization to be out and suspends the transmission when the Ior/Ioc is lower than a reference value Qout for 160 [ms]. Furthermore, the portable terminal judges that the synchronization is established again and resumes the transmission when the Ior/Ioc is higher than a reference value Qin for 160 [ms].
The portable terminal may use SIR (Signal to Interference power Ratio) , which is measured at every frame, instead of the DPCCH_Ec/Ior to judge whether the synchronization is established or not. In this case, reference values for the SIR are obtained by converting the reference values Qout and the Qin for the DPCCH_Ec/Ior.
Hereinafter, the reference values of the SIR are renamed to Qout and Qin. That is, it is assumed that the synchronization judgment is executed by comparing the SIR with the Qout and the Oin. In addition, it is assumed that a period of 160 [ms] is equal to 16 frames. On the condition, the portable terminal operates as follows.
The portable terminal judges the synchronization to be out and suspends the transmission when the measured SIR is lower than the reference value Qout for 16 frames. Furthermore, the portable terminal judges that the synchronization is established again and resumes the transmission when the measured SIR is higher than the reference value Qin for 16 frames.
The SIR has dispersion (or short time variation) even during a short time such as one frame. Especially, the dispersion of the SIR becomes large when the portable terminal moves and/or communication environment is bad.
A related portable terminal meeting specifications of the W-CDMA system judges synchronization to be out and suspends transmission when the measured SIR is lower than the minimum SIR (i.e. Qout), which is decided to keep a call connection, for 16 frames. Furthermore, the related portable terminal meeting specifications of the W-CDMA judges that the synchronization is established again and resumes the transmission when the SIR is higher than the reference SIR (i.e. Qin), which is decided to connect a call, for 16 frames.
Even if the SIR is lower than the reference value Qout for the most part of continuous 16 frames, there is a case where the portable terminal continues the transmission. This is because the SIR exceeds the reference value Qout in a moment when it has large dispersion. Similarly, there is a case where the portable terminal does not resume the transmission when the SIR is higher than the reference value Qin for the most part of 16 frames. This is because the SIR deteriorates under the reference value Qin in a moment when it has the large dispersion.